Abstract
A comprehensive set of physicochemical variables in near-bottom water and surface sediments, as well as the soft-bottom macrozoobenthic assemblages were investigated at six sites across the Yundang Lagoon (Southeast China) in November 2012. This lagoon was severely damaged in the 1970s due to domestic and industrial pollution and land reclamation and underwent a massive restoration effort over the past 30 years. Our objectives were to: (1) assess the current trophic and environmental condition of the lagoon; (2) investigate the pattern of spatial variation in the macrozoobenthic assemblages; and (3) assess the benthic recovery in relation to the main environmental gradients and the presence of invasive alien species. Nutrient, chlorophyll-a, biological oxygen demand (BOD5), chemical oxygen demand (CODMn), and total organic carbon (TOC) concentrations were lower than those reported in previous decades, yet organically-enriched conditions occurred at an inner site. From azoic conditions in the 1980s and a few benthic species reported prior to this study, we found a significant increase in benthic diversity with 43 species heterogeneously distributed across the lagoon. The invasive bivalve Mytilopsis sallei was the dominant species, which was associated with the richest benthic assemblage. However, M. sallei is a pest species, and its spatiotemporal distribution should be carefully monitored. These results highlight the central role of the macrozoobenthos in providing important ecological information on the current status of the Yundang Lagoon and as an effective biological tool to follow the recovery’s progress and the future evolution of this highly valued ecosystem.
Highlights
Coastal lagoons are typically human-managed, highly productive ecosystems which provide multiple uses and services [1,2,3]
Canonical correspondence analysis (CCA) was performed on macrozoobenthos abundance data and environmental variables at each site, in order to test the response of the macrozoobenthic community to the main environmental gradients to determine what provided the best combination of variables supporting the ordination model [42]
Nitrate, ammonium, and RP for the water and total organic carbon (TOC) for the sediments were used as trophic variables, while SS for the water and sand and median particle diameter (Md) for the sediments were used as variables related to the hydrodynamics and confinement of the lagoon
Summary
Coastal lagoons are typically human-managed, highly productive ecosystems which provide multiple uses and services [1,2,3]. Dystrophic events are the cause of anoxia, sulfide development, mass mortalities, and shifts to alternative ecohydrological states characterized by reducing conditions and lower pH [12,13,14,15] Within this context, the concept of “saprobity”, originally developed for rivers and lakes more than a century ago [16,17], applies well to coastal lagoons as a “state descriptor” of the ecosystem’s condition resulting from the input and decomposition of OM and the removal of its catabolites [18]. OM input associated with low saprobity due to high oxygen availability or low by-product (e.g., ammonia and sulfide) concentrations can promote the vitality of the biocoenosis, increasing biomass and abundance
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